12. Clusters of Galaxies - INAFddallaca/RadioA_12_Clusters.pdf“Structures and components in galaxy clusters: observations and models” ... ☞ origin from gas sloshing in the cluster

12. Clusters of Galaxies

a. Feretti, Giovannini, Govoni & Murgia, 2012, A&ARev. 20, 54 “Clusters of galaxies: observational properties of the diffuse radio emission”a'. van Weeren & al. 2019, Space Sci Rev (2019) 215:16 “ Diffuse Radio Emission from Galaxy Clusters”

b. Bykov & al., 2015 SSRv, 188,141 .... or.... https://arxiv.org/pdf/1512.01456.pdf “Structures and components in galaxy clusters: observations and models”

c. Brunetti & Jones, 2014, Int. J. of Mod. Phys D. 23, 30007-30083 “Cosmic Rays in Galaxy Clusters and their Non-Thermal Emission”

a. observational point of viewc. theory & astrophysicsb. link between a and c.

Optical view of Clusters of Galaxies (Hubble) ⇨ STARS (3-5% of the total mass)

Abell 2218, @ z = 0.17

Optical view of Clusters of Galaxies (Hubble) ⇨ GAS (12-15% of the total mass)

Chandra X-ray view of the Perseus clusterhttps://scitechdaily.com/astronomers-discover-a-giant-wave-of-hot-gas-rolling-through-the-perseus-galaxy-cluster/

Full view of Clusters of Galaxies ⇨ Dark matter, gas and stars

APOD 2006 August 24: The Bullet Cluster @ z = 0.296

Clusters of Galaxies

Some facts:

Sizes: roundish, about a few Mpc in radius

Masses: 10 14 – 10 15 M⊙

Galaxies: 100s to 1000s (defnition of either “individual” or “satellite” galaxy for the smallest ones) Mostly ellipticals, then spirals, generally “ISM defcient”

Gas: hot (several KeV) and tenuous (ne ~ 10 – 1 – 10 – 4 cm – 3 )

Dark Matter: 70/80% of total mass, gravitational effects (weak/strong gravitational lensing, σ v

)

Tracers: Gas ⇨ X-rays (Bremsstrahlung) + SZ with CMB in mm, Galaxies ⇨ optical (BB), Dark Matter⇨image distortion on background objects

ASSEMBLY via merger-trees: very massive clusters at z=0 were much lighter at z=1 or beyond ⇨ the effects of mergers may be used to test a lot of physics


All clusters are X-ray emitting extended sources (IGM gas cooling time longer than the Hubble time)

Classifed as:

RELAXED: hydrostatic equilibrium with spherical distribution, very effcient cooling where the gas is denser (cool core clusters), producing enhanced X-ray emission at the center

UNRELAXED: a recent perturbation (minor/major merger) broke the equilibrium heating the gas. About 1 Gyr required to settle down again. X-ray emission is affected

ASSEMBLY via merger-trees: very massive clusters at z=0 were much lighter at z=1 or beyond ⇨ the effects of mergers may be used to test a lot of physics

Disrupt relaxed structures

Very energetic processes, can dump a lot of kinetic energy 10 63 erg to be transferred (in a crossing time of ~ 1 Gyr) to various elements, including relativistic particles and magnetic feld amplifcation


RELAXED: hydrostatic equilibrium with spherical distribution, very effcient cooling where the gas is denser (cool core clusters), producing enhanced X-ray emission at the center

UNRELAXED: a recent perturbation (minor/major merger) broke the equilibrium heating the gas. About 1 Gyr required to settle down again. X-ray emission is affected

ILLUSTRIS view of Clusters of Galaxies

Large scale projection through the Illustris volume at z=0, centered on the most massive cluster, 15 Mpc/h deep. Shows dark matter density (left) transitioning to gas density (right).

ILLUSTRIS view of Clusters of Galaxies

Simulation of a merger: F. Vazza

https://vimeo.com/307848975

Radio view of Clusters of Galaxies: ~ local people involved in “radio science “

Simona Giacintucci (Naval Research Lab), Matteo Angelinelli, Serena Banf, Nadia Biava, Luca Bruno, Alessandro Igniesti, Nicola Locatelli, Chiara Stuardi (PhD)Kamlesh Rajpurohit, Chris Riseley, Gianadrea Inchingolo, Marisa Brienza, Etienne Bonnassieux (posdoc)+ Xrays.....

4

Combined B and C confguration radio map of J00560226+2627287 at a central frequency of 6 GHz.

The restoring beam is 1”. (Harwood +, 2015)

Radio view of Clusters of Galaxies

Radio emission from: Individual galaxies (+ Diffuse sources)

Radio Galaxies:➢ A number of “compact radio sources”

➢ Extended objects are typically FR – I radio galaxies with distorted morphology (cluster weather)

WAT NAT

3C465


Radio emission from: Individual galaxies (+ Diffuse sources)

Radio Galaxies:➢ A number of “compact radio sources”

debate whether the cluster triggers/quenches the radio activity

● Extended objects are typically FR – I radio galaxies with distorted morphology (cluster weather)Radio power determines the FR-type, as well as the lack of hot-spots

● Often the BCG has substantial radio emission (despite it might not be the brightest radio source of the cluster)

● AGN feedback: Heating the ICM Interaction between thermal and non-thermal plasma

● There is a well established infuence of the dynamical status of the cluster on what we observe

● Remember that we stated that spiral galaxies in clusters are HI defcient (e.g. Haynes & Giovannelli 1984)

Radio view of Clusters of Galaxies: Diffuse sources

Diffuse sources (defnition & properties)

● Not associated to an optical host

● Rather large (LS ≥100s kpc, sometimes exceeding the Mpc)

● Steep radio spectrum (α ≥1.2 – 1.3 )

● Typical surface brightness @ 1.4 GHz is ~ 1 µJy/arcsec 2 (i.e. their large (LLS & LAS) and the relatively weak fux density give low surface brightness)

● They can be in the form of radio ... ● ...HALOs,● ...mini-HALOs, ● ...RELICs (shocks, phoenices, GReETs)

Radio view of Clusters of Galaxies: Diffuse sources and the diffusion problem

ABELL 2744Left: X-ray (Chandra 0.5-2.0 keV) and optical (Subaru) photonsRight: Radio (JVLA 1 – 4 GHz) and optical emission (picture from van Weeren +2019)


The linear sizes of diffuse radio sources cannot be covered by (relativistic) plasma transfer(diffusion) during the radiative lifetime of the particles.

t syn

~ 10 7 – 10 8 yr

With particles bulk motions of v ~ 0.1 c they could travel 10 6 – 10 7 light-yr (max 10s of kpc)

Re-acceleration processes are required : IN – SITU

Mechanisms should produce a large number of “fresh” relativistic electrons ( and processes providing energy should be found):

Shocks, Turbulence, DSA in generalDetails of re-acceleration mechanisms (frst / second order Fermi acceleration; “secondary models), (adiabatic) Compression ...


● Radio Mini-Halo● ☞ a few hundreds of kpc in size, roundish, centrally located ● ☞ likely associated with the cD galaxy ● ☞ in Cool Core Clusters (CCC)

● (Giant) Radio Halo ● ☞ cluster wide, 1-2 Mpc in size ● ☞ smooth and roughly centered on the galaxy distribution & X-ray emission● ☞ P

1.4 GHz ~ 3.1 x10 23 ↔ 1.6 10 26 W Hz – 1

● ☞ unpolarized, generally (very) steep spectrum (α ≥ 1.3 ), uniformly distributed ● ☞ in dynamically “active”/”disturbed” clusters● ☞ “El Gordo”, at z=0.87 is the most distant

● Radio Relic● ☞ Shock (elongated, up to ~ Mpc long, peripheral regions, often substantially polarized)● ☞ Phoenix (elongated, up to ~ Mpc long, peripheral regions, often substantially polarized)● ☞ GReET (Gently Re-Energized Tail)

AGN feedback:➢ Heating the ICM➢ Interaction between thermal and non-thermal plasma

Radio view of Clusters of Galaxies: Diffuse sources: Radio Mini-Halo

● ☞ a few hundreds of kpc in size, roundish, centrally located, sometimes diffcult to be classifed ● ☞ in Cool Core Clusters (80 % of CCC host a mini-halo, 0% in non CCC)● ☞ in ~50 % of X-ray luminous clusters L

X (0.1-2.4 keV) > 5 x 10 44 erg s – 1) at 0.2 < z < 0.4

● ☞ likely associated with the cD galaxy (AGN contribution may be diffcult to be highlighted)● ☞ Often “cavities” in the IGM/ICM● ☞ P

1.4 GHz ~ 10 23 ↔ 10 25 W Hz – 1

● ☞ the most distant at z=0.805 (uncertain) ● ☞ emissivity higher than in Giant RH (emissivity mostly confned to the X-ray cooling region)● ☞ local spectral index quite uniform (very incomplete info), integrated ~ power-law● ☞ unknown polarization properties● ☞ origin from gas sloshing in the cluster core (fossil electrons from the central AGN)

● Radio emission with a spiral-shape like tail and hints of steepening along the tail in RXJ1720.1+2638(Giacintucci + 2014)


Feedback: interaction between relativistic and thermal plasmas


Feedback: interaction between relativistic and thermal plasmas

Gendron-Marsolais + 2017, VLA image 230-470 MHz, beam ~22x11”

Radio view of Clusters of Galaxies: Diffuse sources can be:

Radio Mini-Halo (a few hundreds of kpc in size, likely associated with the cD galaxy)

AGN feedback:➢ Heating the ICM➢ Interaction between thermal

and non-thermal plasma

http://inspirehep.net/author/profile/Gendron-Marsolais%2C%20M.?recid=1509181&ln=en

Chandra X-ray view of the Perseus clusterhttps://scitechdaily.com/astronomers-discover-a-giant-wave-of-hot-gas-rolling-through-the-perseus-galaxy-cluster/

Radio view of Clusters of Galaxies: Diffuse sources can be:

Radio Mini-Halo (a few hundreds of kpc in size, likely associated with the cD galaxy)

https://www.nasa.gov/feature/goddard/2017/scientists-fnd-giant-wave-rolling-through-the-perseus-galaxy-cluster

Detailed information and a movie from numerical simulation on how the “spiral like structure” is formed.

https://www.nasa.gov/feature/goddard/2017/scientists-find-giant-wave-rolling-through-the-perseus-galaxy-cluster

Radio view of Clusters of Galaxies: What happens is a merger breaks down the “quiet cluster”?

CCC may be disrupted by [major) merger (unclear how long the CCC may survive after the start of the merging) [minor merger might not be able to a full disruption]

The same applies to the Radio Mini-Halo (?)

Particles may be transported outer regions and reaccelerated ( Giant RH)

In minor merger both mH and GRH may coexist A handful of objects may be interpreted as mH + GRH

Strong cosmological evolution The merger history is very time-dependent: big clusters are more easily found at z~0 since the

mass assembly proceeds as the Universe evolves For diffuse radio emission from relativistic electrons, the IC with CMB photons is getting more

and more relevant [“ H CMB

” ~ 3.28 (1+z) 2 μ G ]

Radio view of Clusters of Galaxies: cartoon of cluster merger

Numerical simulations show that an equatorial shock is formed frst when there is the frst passage at thebarycenter. This is a “belt”, best visible at the edges where the LoS intercepts a larger layer of particles

Subsequently, Turbulence

Radio view of Clusters of Galaxies: Diffuse sources: (Giant) Radio Halos

● ☞ cluster wide, 1-2 Mpc in size ● ☞ smooth and roughly centered on the galaxy distribution & X-ray emission● ☞ P

1.4 GHz ~ 3.1 x10 23 ↔ 1.6 x 10 26 W Hz – 1

● ☞ unpolarized, generally (very) steep spectrum (1.1 ≤ α ≤ 1.4), uniformly distributed ● ☞ in dynamically “active”/”disturbed” clusters● ☞ “El Gordo”, at z=0.87 is the most distant● ☞ about 75 GRHs are known to date ( may 2020)

Abell 2255(point source subtracted) Radio image and grid [relic non included]

Govoni et al. 2001


Blue: X ray emission

Red: radio emission

Excluding individual (and foreground/background)radio sources, the diffuse emission is co-spatialto thermal plasma

Often the foreground/background radio sourcesare diffcult to disentangle from the extendedradio emission, leading to uncertainties in the determination of the properties of each class.


Spectral index:

Local (in situ) distribution [uniform] & Integrated spectrum [steepening]

Models predict that a USSRHpopulation should exist (see further)

Clusters of Galaxies :Radio Halo sources: Radio .vs. X-ray Luminosity Correlation (Radio Luminosity .vs. Mass)

Clusters of Galaxies :Radio Halo sources: Radio .vs. X-ray Luminosity Correlation (Radio Luminosity .vs. Mass)

Radio view of Clusters of Galaxies: Diffuse sources: Shocks

Radio Relic (elongated, up to ~ Mpc long, peripheral regions, often substantially polarized)

⇐ Relic(s) and Giant Radio Halomay coexist and may be overlapping(bridged)

X-ray view of Clusters of Galaxies: signatures of dynamical activity

Shocks traced by the outer limb

Steepening due to ageing

Polarization!

Mach number from αinj

M = √ 2αinj−32αinj+1

= √ 2αinj+32αinj−1

for S(ν) ≈ να \\===// S(ν) ≈ ν−α respectively

Actively accelerated particlesAgeing particlesAged particles

Searching for a “hot topic” in radio astronomy

Detailed morphological/polarization studies of individual relicsToothbrush: flamentary structure: why? Changes in B?


Jumps in Surface Brightness, T, ne ⇨ SHOCKS

(Ghizzardi +, 2010)


How to detect discontinuities:

Jumps in Surface Brightness, T, n

e

⇨ SHOCKS





from Rankine-Hugoniot conditionsTd

Tu

= 5 M 4+14 M 2−316 M 2

ρdρu

= C = 4 M 2

M 2+3M is the Mach number

“Hot topic”: newly discovered UUSS radio sources: Phoenices

Low frequencies sample “long living” electronswith relatively modest γ .

Sources visible below 200 MHzMust have a sharp cutoff

Old population of “dying” electrons ?Fossil electrons revived by some process?

“Hot topic”: newly discovered UUSS radio sources: Gently ReEnergized Tailed sources [ GreETs ]

Low frequencies sample “long living” electronswith relatively modest γ .

These particles are border-line with beinginsterted into the CR travelling in the cluster

Some may be the seed particles to be accelerated

“Hot topic”: newly discovered UUSS radio sources: Gently ReEnergized Tailed sources [ GreETs ]

Spectral index map of the radio emission in Abell 1033.(Left) Spectral index values (142 to 323 MHz) of the radio emission. To trace the evolution of the spectral index along the tail of the WAT radio galaxy,we defned 20 beam-sized regions. (Right) Each point in the plot is associated with one region defned in the left panel. Lines show the spectral index and the 142-MHz fux density predicted by a model, assuming three possible values for the magnetic feld. The position of point 1 has been shifted on the x axis to match the model spectral index for the 2.3-μG case, and the age axis has been stretchedto ft the spectral index data (refecting the unknown galaxy speed). Star markersin the plot show the expected spectral index and fux density if a gentle reaccelerationstarts at 450 My. Green stars assume no projection effect, while yellow stars assume a 40° inclination of the tail with respect to the line of sight. (from De Gasperin et al. 2017)

Radio view of Clusters of Galaxies: Acceleration of relativistic particles

Acceleration of seed electrons

1. from the “thermal pool”2. pre-esisting CRs3. fossil plasma

Via Shocks (i.e. mainly Fermi – I) and Turbulence (mainly Fermi - II)

4. secondary electrons (+ positrons) Gamma rays from 0 decay are expected but not observed so far. Upper limits in FERMI and ground based observation imply at most a few % in terms of their contribution to the totale energy content.


Brunetti & Jones (2014)


Brunetti & Jones (2014)

Balance between acceleration & energy losses (radiative, expansion, etc)

1 – 3 GHz100 – 300 MHz

Clusters of Galaxies :Radio Halo sources: standard and Ultra Steep – Spectrum (Brunetti + 2008, Nature)

Log Frequency

Log P

R

Conventional RH: α ~1.3

USS RH: α ~ 1.8 – 2.0

Major

Merger

Minor

Radio view of Clusters of Galaxies: Summary (1)

Mini-Halo: electrons from AGN (cD); sloshing possibly plays a role

Radio Halo: turbulent acceleration as from mergers

Radio Relic: low M shock acceleration of fossil plasma

● Diffusion time (e.g. for CR) is ~ 10 9 yr, exceeding the radiative lifetime (~10 8 yr)

➢ Need for: in situ (re – ) acceleration of electrons ➢ What about their origin? Primary/Secondary e– ? Fossil plasma? ... implications (see Brunetti & Jones) ... Longstanding debate, many questions still open

➢ Relaxed clusters may host a mini-halo➢ Merging clusters may host a radio-halo and/or radio relic(s)

● Energy from mergers converted into particle acceleration via low M shocks● Spectral index of the halo depending on the mass ratio and total energy (Normal .vs. USS RH)

Radio view of Clusters of Galaxies: Summary (2)

Radio Halo sources➢ Low surface brightness

➢ Steep spectral index ( ~ 1.3, but also 1.8-2.0 -> USSRH), relatively uniform across the whole radio emittingregion

➢ No polarization

Relic radio sources➢ Elongated, at peripheral regions of clusters. Active acceleration surface best visible.

➢ SPIX gradient from ~1.0 to 1.5 and more.

➢ Polarized!

Steep synchrotron radio spectrum: ALL are best studied at low frequencies (e.g. LOFAR!) given the steepspectral index and uv-coverage of Interferometric observations.

Radio view of Clusters of Galaxies: Extended time! Abell 2256: A relic which is not seen edge on?

JVLA spectral index image (1-8 GHz), resolution of 6” (Owen + 2014)

LOFAR radio continuum emission at 120-180 MHz of Abell 2256. The resolution is 5 arcsec and the image has a noise about 0.1 mJy/beam (van Weeren + 2015)

Radio view of Clusters of Galaxies: Extended time! Abell 2256: A relic which is not seen edge on?

Radio halo and a lot of steep spectrum radio emission show up!

Searching for a “hot topic” in radio astronomy (1)

MACS J0717.5+3745

Searching for a “hot topic” in radio astronomy (2)

Abell 1682 @ z = 0.2259

Individual radio galaxies & diffuse emissionLow-frequency tails are relic emission? A new active cycle has begun in the AGN?Fossil plasma accelerated by turbulence?

Left: LOFAR image at ~ 145 MHz, 5” resolution Right: VLA A-array image at 1.46 GHz, downgraded to 4” resolution

Left: VLA A-array 1.46 GHz, 1.3” resolution. Right: optical (DSS) ~ 2” resolution


Abell 1682 @ z =0.2259

LOFAR image at ~ 145 MHz, 5” resolution

Steep – Spectrum radio flaments/threads:evidence for turbulent acceleration. No counterpart at high frequencies

EXAMPLE: of “hot topic” in radio astronomy: El Gordo cluster at z=0.87, and relic – shock connection

Botteon et al. 2016The X-ray SB profle abruptly drops at the relic location.The density compression factor C ~ 3 and the high downstream temperatureprovide the indication of a strong shock (M ~ 3) in the ICM.This is one of the three strongest shocks detected in galaxy clusters and themost distant (z = 0.87) observed so far. The detection of a shock co-spatially located with a relic strongly supports the relic–shock connection. The NW shock in ‘El Gordo’ cluster allows to study particle acceleration in a rare regime of strong shock. DSA of thermal electrons is consistent with measured synchrotron spectrum. Nonetheless, only shocks with M > 3.5 appear energetically viable while for weaker shocks re-acceleration models would be preferred.The presence of relativistic particles emitting a bright synchrotron relic at z = 0.87 makes ‘El Gordo’ a suitable cluster candidate to search for IC emission from the relic.From the X-ray spectral analysis we obtained possible hints for IC emission fromthe relic, however we could not frmly conclude the presence of IC excess andconservatively we derived only lower limits to the downstream magnetic feld that have been used to improve constraints on particle acceleration. However, we also found hints of an excess in the 0.5-2 keV SB profle across the relic region. The combination of a possible IC excess in the spectral analysis with the hints ofexcess in the SB is tantalizing and certainly deserves deeper Chandra observations.


Summary of the summary.

➢ Defnition/CompositionDark matter, galaxies, gas (thermal & relativistic components), magnetic feld

➢ Relevant parameters Mass & LuminosityMorphological Classifcation (Relaxed .vs. Unrelaxed. Radio galaxies, environmental infuence, BGC emission, NAT & WAT )

➢ Astrophysical problems:Diffusion time for relativistic particlesTotal energy content (CR, H, Thermal)

➢ Particle acceleration (low Mach numbers, large regions: DSA .vs. Reacceleration) and shocks (cold fronts)

➢ Beyond the suggested literature for the exams, search for the papers by Bonafede, Botteon, Brunetti, Cassano,Cuciti, Vazza, (LOFAR), etc

Possible topics for a thesis in radio astronomy (partial selection, incomplete list of local people)

➢ Masers (Arcetri, J. Brand)

➢ Radio stars (Catania)

➢ Pulsars (Cagliari)

➢ SNR

➢ Microquasars (G. Migliori)

➢ AGN (M. Orienti, M.Giroletti, F. D'Ammando)

➢ ALMA (V. Casasola, F. Pozzi, A. Cimatti, R. Paladino, E. Liuzzo, M. Massardi)

➢ Radio galaxies (T. Venturi)

➢ Clusters of Galaxies (A. Bonafede, G. Brunetti, R. Cassano, T. Venturi, M. Gitti, F. Brighenti, F. Vazza, S. Ettori,G. Giovannini)

➢ Survey & radio counts (I. Prandoni, M. Bondi)

Documents

12. Clusters of Galaxies - INAFddallaca/RadioA_12_Clusters.pdf“Structures and components in galaxy clusters: observations and models” ... ☞ origin from gas sloshing in the cluster